Molten-salt-heated indirect screw-type thermal processor

Abstract

A body of heat transfer fluid circulates in a first loop through an indirect screw-type thermal processor, a rundown tank, a pump, a heater and a fill tank, continuously heating the processor. With the pump operating, a first vertical distance between the fill tank bottom and the processor under the influence of gravity sets a minimum fluid pressure at the processor; a stem pipe opening in the fill tank at a second vertical distance above the processor sets a maximum pressure. With the pump inactive, the entire body of fluid passively drains to the rundown tank. Supplying the fluid may entail melting a salt, hydrating a salt, or both; such may be done in the rundown tank before circulation through the processor begins. A hydrated salt may be circulated, then heated and dehydrated, to gradually warm the processor. A dehydrated salt may be rehydrated and then stored; this may be done in the rundown tank after ceasing circulation through the processor. Also described: misting hydration and variable-speed-pump pressure regulation.

The invention claimed is: 
     
       1. Molten-salt-indirectly heated screw-type thermal processing apparatus, comprising:
 an indirectly heated screw-type thermal processor; a heater; a rundown tank; and a pump, 
 the apparatus requiring an operating volume of a heat transfer fluid for transferring heat from said heater to said thermal processor, 
 said thermal processor having a heat transfer fluid inlet fluidly communicating with said heater and a heat transfer fluid outlet fluidly communicating with said rundown tank, 
 said rundown tank having a fluid-containing portion dimensioned to hold at least said operating volume and having a rundown tank headspace portion above said fluid-containing portion, said rundown tank headspace portion being equipped to relieve a pressure differential between said rundown tank and the ambient environment, 
 said pump, said heater, said thermal processor and said rundown tank being operatively connected so as, when said pump is active, to establish a heat transfer circulation loop through said heater and said thermal processor, 
 said pump, said heater, said thermal processor and said rundown tank being operatively connected so as, when said pump is inactive, to establish said fluid-containing portion as the fluid passive drainage destination relative to said pump, said heater and said thermal processor; 
 the apparatus having a gravity tube, a gravity tube upper drain, a gravity tube gas orifice, and a gravity tube lower drain, 
 said gravity tube fluidly communicating with said heat transfer fluid inlet at a first height, 
 said gravity tube fluidly communicating with said heater at a second height, said second height being above said first height 
 said gravity tube upper drain fluidly communicating with said gravity tube at a third height, said third height being above said second height, 
 said gravity tube upper drain fluidly communicating with said rundown tank, 
 said gravity tube gas orifice fluidly communicating with said gravity tube at a fourth height, said fourth height being above said third height, 
 said gravity tube gas orifice fluidly communicating with said rundown tank headspace portion, 
 said gravity tube lower drain fluidly communicating with said gravity tube at a fifth height, said fifth height being below said first height, 
 said gravity tube lower drain fluidly communicating with said rundown tank at a sixth height, said sixth height being below said fifth height. 
 
     
     
       2. Apparatus of  claim 1 , having a restrictor located in said gravity tube lower drain at a seventh height, said seventh height between said fifth height and said sixth height, said restrictor being dimensioned to restrict fluid conducting capacity of said gravity tube lower drain. 
     
     
       3. Apparatus of  claim 1 , having a fill tank and a stem pipe,
 said fill tank communicating with said gravity tube at said second height, 
 said stem pipe fluidly communicating with said fill tank at said third height and fluidly communicating with said gravity tube upper drain. 
 
     
     
       4. Apparatus of  claim 1 , selectively configurable to establish a preheating fluid circulation loop through said rundown tank and to interrupt said heat transfer circulation loop. 
     
     
       5. Apparatus of  claim 1 , adapted for a heat transfer fluid having a melting point and a density, said first height and said second height being selected such that a column of said heat transfer fluid extending vertically from said first height to said second height exerts pressure at said second height no greater than 14.9 PSIG when said fluid is at said melting point. 
     
     
       6. Apparatus of  claim 1 , having a pressure sensor proximate said heat transfer fluid inlet of said thermal processor and a pump variable speed control, said pump variable speed control being operatively coupled with said pressure sensor so as to slow said pump when said pressure sensor reports a pressure exceeding a predetermined setpoint below 14.9 PSIG. 
     
     
       7. Apparatus of  claim 1 , wherein said heat transfer fluid outlet is located above said first height. 
     
     
       8. Molten-salt-indirectly heated screw-type thermal processing apparatus, comprising:
 an indirectly heated screw-type thermal processor; a heater; a rundown tank; and a pump, 
 the apparatus requiring an operating volume of a heat transfer fluid for transferring heat from said heater to said thermal processor, 
 said thermal processor having a heat transfer fluid inlet fluidly communicating with said heater and a heat transfer fluid outlet fluidly communicating with said rundown tank, 
 said rundown tank having a fluid-containing portion dimensioned to hold at least said operating volume and having a rundown tank headspace portion above said fluid-containing portion, said rundown tank headspace portion being equipped to relieve a pressure differential between said rundown tank and the ambient environment, 
 said pump, said heater, said thermal processor and said rundown tank being operatively connected so as, when said pump is active, to establish a heat transfer circulation loop through said heater and said thermal processor, 
 said pump, said heater, said thermal processor and said rundown tank being operatively connected so as, when said pump is inactive, to establish said fluid-containing portion as the fluid passive drainage destination relative to said pump, said heater and said thermal processor; 
 the apparatus having a fluid hydrator and a hydration fluid supply, said fluid hydrator fluidly communicating with said heat transfer circulation loop and with said hydration fluid supply, 
 said hydration fluid supply being selected from among a supply of water, a supply of steam, and a supply of a hydrating solution; 
 said fluid hydrator being configured to deposit a hydration fluid in said rundown tank. 
 
     
     
       9. Apparatus of  claim 8 , said fluid hydrator comprising a nozzle, said nozzle being located in said rundown tank headspace portion and being configured to deposit a hydration fluid in said rundown tank. 
     
     
       10. Apparatus of  claim 8 , said fluid hydrator comprising a sparge tube located in said fluid-containing portion of said rundown tank. 
     
     
       11. Apparatus of  claim 8 , said fluid hydrator comprising an eductor. 
     
     
       12. Molten-salt-indirectly heated screw-type thermal processing apparatus, comprising:
 an indirectly heated screw-type thermal processor; a heater; a rundown tank; and a pump, 
 the apparatus requiring an operating volume of a heat transfer fluid for transferring heat from said heater to said thermal processor, 
 said thermal processor having a heat transfer fluid inlet fluidly communicating with said heater and a heat transfer fluid outlet fluidly communicating with said rundown tank, 
 said rundown tank having a fluid-containing portion dimensioned to hold at least said operating volume and having a rundown tank headspace portion above said fluid-containing portion, said rundown tank headspace portion being equipped to relieve a pressure differential between said rundown tank and the ambient environment, 
 said pump, said heater, said thermal processor and said rundown tank being operatively connected so as, when said pump is active, to establish a heat transfer circulation loop through said heater and said thermal processor, 
 said pump, said heater, said thermal processor and said rundown tank being operatively connected so as, when said pump is inactive, to establish said fluid-containing portion as the fluid passive drainage destination relative to said pump, said heater and said thermal processor; 
 the apparatus being equipped to receive a padding gas from a padding gas supply when said rundown tank is underpressurized relative to the ambient environment.